Apparatus and method for applying radio frequency energy to a moving web of material

ABSTRACT

A moving web of material, preferably of newly formed paper, is diverted from its normal path of travel and directed through a radio frequency drying area and returned to the normal path of progress. Radio frequency electrodes are arranged around an arcuate path which the web of material follows, thereby minimizing the space required to incorporate radio frequency drying into an existing process. The electrode holders have passages formed therein which are connected to a source of heated air. Air is emitted through the electrode holders and acts to form an air film which prevents the web from touching the electrodes or electrode holders. An enclosure around the electrode holder area has a plurality of nozzles attached to its interior portion. The nozzles are connected to a source of heated air, the air emitted from the nozzles acting as a position control device for the web. The air emitted from the nozzles and the air film act in balance to maintain the web at a specified elevation above the electrodes. If the web should break, a pressure-sensitive element within the electrode enclosure senses a decrease in pressure and turns off the radio frequency power to avoid any danger to operating personnel.

United StatesPatent 1191 Marteny I APPARATUS AND METHOD FOR APPLYINGRADIO FREQUENCY ENERGY TO A MOVING WEB OF MATERIAL [75] Inventor:William W. Marteny, Toledo, Ohio [73] Assignee: Owens-Illinois, Inc.,Toledo, Ohio [22 Filed: 1111;; 6, 1971 [21] Appl. No.: 159,630

[52] US. Cl. ..;.....34/l, 34/49, 34/156 [51] Int. Cl. ..B0lk 5/00 [58]Field of Search ..34/l, 49, I56

[56] References Cited UNITED STATES PATENTS 3,629,948 12/1971 Hilton eta1 "34/1 3,559,301 2 1971 Fraser 3,085,347 4/1963 Justus 3,426,439 21969 Ryrnan 6:31.

3,460,265 8/1969 Smith ..34 1

FOREIGN PATENTS OR APPLICATIONS 1,079,677 8/1967 Great Britain ..34 1

Primary Examiner-Carroll B. Dority, Jr. Att0rneyA. J. Steger et a].

1451 Mar. 27, 1973 [57] ABSTRACT A moving web of material, preferably ofnewly formed paper, is diverted from its normal path of travel anddirected through a radio frequency drying area and returned to thenormal path of progress. Radio frequency electrodes are arranged aroundan arcuate path which the web of material follows, thereby minimizingthe space required to incorporate radio frequency drying into anexisting process. The electrode holders have passages formed thereinwhich are connected to a sourceof heated air. Air is emitted through theelectrode holders and acts to form an air film which prevents the webfrom touching the electrodes or electrode holders. An enclosure aroundthe electrode holder area has a plurality of nozzles attached to itsinterior portion. The nozzles are connected to a source of heated air,the air emitted from the nozzles acting as a position control device forthe web. The air emitted from the nozzles and the air film act inbalance to maintain the web at a specified elevation above theelectrodes. If the web should break, a pressure-sensitive element withinthe electrode enclosure senses a decrease in pressure and turnsoff theradio frequency power to avoid any danger to operating personnel.

4 Claims, 3 Drawing Figures BACKGROUND OF THE INVENTION 1. Field of theInvention This invention relates generally to the drying of newlymanufactured paper. More particularly, the invention relates to thedrying of such paper by the use of radio frequency energy. Mostspecifically, the invention relates to an apparatus and method forefficiently incorporating radio frequency drying into an existing papermanufacturing line.

2. Description of the Prior Art The use of radio frequency energy forthe drying of newly formed paper is well known in the art, for example,such drying is taught in [1.8. Pat. No. 3,399,460. However, the use ofelectrical energy to dry paper is relatively expensive compared to theconventional steam-heated drum-type drying used in most paper mills. Ina co-pending application, U.S. Ser. No. 128,959, filed Mar. 29, 197.1and assigned to the same assignee as the subject invention, the use ofradio frequency drying in a particular critical moisture range of paperto obtain maximum efficiency and economy is taught. However, theelectrode systems of the prior art for use in such a scheme, haveconventionally been of an elongated configuration. This has limited theapplicability of radio frequency drying to existing papermaking linesbecause of the difficulties in integrating a relatively long dryingsection in the existing floor plan. In addition, there has always beenthe danger of the wet paper web touching the electrodes and possiblycausing a short circuit in the system. The present invention overcomesthese difficulties by diverting the paper web from its normal path oftravel through an external arcuate electrode configuration and floatingthe web of paper on an airfilm over the electrodes.

SUMMARY OF THE INVENTION This invention discloses an apparatus forapplying I radio frequency energy to a moving web of material,preferably newly formed paper, having a plurality of electrode holdersarranged about the peripheryof an arcuate path followed by the movingweb. The electrode holders carry a plurality of individualelectrodes andare connected to a source of radio frequency energy. The entireelectrode holder and electrode array is enclosed by an arcuate cover,which thereby forms an enclosed volume. Streams of heated air aredirected through passages in the electrode holders to float the web ofmaterial above the electrodes and electrode holders, while acounterstream of heated air is directed from nozzles in the interior ofthe enclosure to balance the air film and thereby hold the web at afixed position above the electrodes and electrode holders. A presofefficiently utilizing radio frequency energy in the selective drying ofa paper web by diverting the web from its normal path of travel into anarcuate path of BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematiccross sectional elevation view of the apparatus of the presentinvention.

,FIG.'2 is a schematic cross sectional elevation view of a portion ofthe apparatus of FIG. 1 at a greater scale than that used in FIG. 1.

FIG. 3 is a sectional schematic view of the apparatus of the presentinvention taken along the line 3-3 in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT It will be apparent to thoseskilled in the paper-making art that the drawings show only a very smallportion of a total'paper-making process. The section shown is one in theconventional steam drum drying sections of a paper-making line. Theparticular point in the line is in the critical moisture range of thepaper web which is disclosed in the previously mentioned co-pendingapplication. As may be seen in FIG. 1, the moving web of paper 10 isdiverted over a roller 11 in an arcuate path. The advantage of thisinvention over the prior art may be readily seen at this point. The webof paper 10 is exposed to radio frequency energy as it passes along thearcuate path of approximately 6 feet in diameter as opposed to thenecessity of having a 12 to 15 foot long linear length of the electrodesof the prior art. The web 10 is thus allowed to bypass the main streamof operating equipment making possible the introduction of selectiveradio frequency energy drying of the web 10 without major modificationsof the existing operating equipment. In this preferred embodiment, acylindrical supporting member 14 serves to define the arcuate pathfollowed .by the paper web 10. However, the actual path followed couldbethat of an inverted U or of a U if a greater length of exposure toradio frequency energy was desired. The support member 14 serves tocarry a plurality of electrode holders 16 arrayed about the periphery ofthe support member 14. The electrode holders 16 are preferably of asmooth, hard inorganic material that will notbe carburized by theelectric field. Furthermore, the electrical properties of the electrodeholders'l6 should be similar to those of air. A material that has beenfound suitable for this purpose is Corning 1991 glass manufactured bythe Corning Glass Works of Corning, N. Y. Each electrode holder 16serves to support an individual electrode 18. It will be noted that theelectrode holders 16 all have a depressed U-shaped channel section neartheir center in which the electrodes 18 rest. Thus, the electrodes 18are depressed below the surface of the electrode holders 16. The arrayof electrode holders l6 and electrodes 18 are surrounded by. anenclosing structure 20 to provide a I sealed volume within which the web10 passes.

travel and floating the paper web over the electrodes 7 which apply theradio frequency energy.

The web 10 is directed in an arcuate path by the roller 11 around theperiphery of the support member 14 and exits from the enclosure around are-entry roller 22 which places the web 10 back into the mainstream ofthe paper-drying process. The enclosure 20 is of a double-walledconstruction to provide a plenum chamber 24 into which heated air underpressure is introduced through inlets 25 and 26 from a heated air source27 through a pressure regulator 23. The electrode holders 16 aresimilarly mounted over a second plenum chamber 23, which is a part ofthe support member 14, the plenum chamber 23 being fed hot air underpressure from the heated air source 27, through an outlet line 29connected to inlet members 30 and 31.

Turning now to FIGS. 2 and 3, it will be seen that a series of passages32 are drilled through the electrode holders l6 and communicate with thesecond plenum chamber 28. As air is introduced into the second plenumchamber 28 through the inlets 30 and 31, this air exits through thepassages 32 through the electrode holders 16. The result of this airflow is to provide an air film over the electrode holders 16 upon whichthe paper web 10 floats. That is, as the paper web 10 passes through itsarcuate path from the diverting roller 11 to the re-entry roller 22, itis never allowed to touch the surface of the electrode holder 16, butrather floats a short distance away from the upper surface of theelectrode holders 16. Communicating with the plenum chamber 24 are aplurality of nozzles 34 which allow the air from the plenum chamber 24to be directed against the upper surface of the paper web 10. Thus, asclearly seen in FIG. 2, there is a balancing effect between the airemitted from the nozzles 34 and the air emitted from the passages 32which holds the paper web 10 at a particular elevation above theelectrode holders 16. By varying the pressure differential between thetwo air flows, the elevation of the paper web 10 above the electrodeholders 16 may be adjusted for varying conditions. The air pressure ofthe air emitted by the nozzles 34 is controlled by adjustment of thepressure regulator 23 which feeds the two inlet lines 25 and 26. Aspreviously noted, the air introduced into the plenum chambers 24 and 28is preferably air heated to a temperature above that of the ambient air.The heated air helps remove any moisture which is driven from the paperweb 10 during the application of radio frequency energy and helpsprevent any condensation on the electrodes 18 or the electrode holders16 which might lead to electrical short circuits in the radio frequencyenergy circuit.

As a safety measure, a pressure-sensitive switch 36, shown in FIG. l, isused to sense the pressure in the plenum chamber 28. So long as thepaper web 10 is continuously passing over the plurality of electrodeholders 16, a particular back pressure will be generated in the plenumchamber 28 due to the interference of the paper web 10 with the freeexit of air from the passages 32 in the electrode holders 16. Should thepaper web 10 break while traversing the arcuate path about the electrodeholders 16, the pressure within the plenum chamber 28 would experiencean immediate drop, due to the lack of back pressure caused by thepresence of the paper web 10. The pressure sensitive switch 36 isconnected to a radio frequency energy generator 37 by suitable wiring 35and will turn off the radio frequency energy in the event a break occursto prevent any possible exposure of operating personnel to the dangerousradio frequency energy. As shown best in FIG. 3, the nozzles 34connected to the plenum chamber 24 are not only arrayed about theperiphery of the enclosure but also extend across the width of theenclosure 20. Similarly, the passages 32 through the electrode holders16 also extend across the entire width of the electrode holder 16. This,of course, is necessary because of the substantial width of the paperweb 10 which passes through this apparatus. Also seen most clearly inFIG. 3 are two extending vertical bosses 38 and 39 on the ends of theelectrode holders 16. These bosses are drilled through so that theelectrode 18 may be inserted through the bosses 38 and 39 and held inposition in this manner in the channel formed in the electrode holder16. It will be noted that the electrodes 18 extend beyond the ends ofthe electrode holders 16 to allow connection to the source of radiofrequency energy 37 in a conventional and well known manner by suitablewiring means 41 and 42. Also, it may be seen that the air which comesfrom the plenum chamber 28 through the passages 32 in the electrodeholder 16 and the air which comes from the plenum chamber 24 through thenozzles 34 is exhausted from the enclosure 20 through exhaust manifolds40 which close the ends of the enclosure 20 and complete the enclosedvolume of the radio frequency energy applying area. Thus, the moistureladen air from the enclosed volume is removed to insure that there willbe no condensation on the electrodes 18.

What I claim is:

1. The method of applying radio frequency energy to a moving web ofmaterial comprising the steps of diverting said web from its normal pathof travel into an arcuate path, floating said web on an air film over aplurality of electrodes located about the periphery of said path,applying radio frequency energy to said web from said electrodes as saidfilm floats over said electrodes, sensing the pressure of said air film,signaling a decrease in the pressure of said air film, discontinuingapplication of said radio frequency energy in response .to saiddecreased pressure signal, and returning said web to its normal path oftravel.

2. The method of claim 1, further including the steps of directing airat said web on the side of said web opposite said air film through aplurality of air emitting nozzles, and positioning said web above saidelectrodes in response to the pressure differential between said airfilm and the air directed by said plurality of nozzles.

3. The method of Claim 2 wherein said air in said air film and said airdirected through said air emitting nozzles is heated to a temperaturegreater than ambient air temperature.

4. Apparatus for applying radio frequency energy to a moving web ofmaterial directed in an arcuate path comprising, in combination: anarcuate supporting member defining the arcuate path for said web; aplurality of electrode holders arranged about the periphery of saidarcuate supporting member, each of said electrode holders having aplurality of passages formed therethrough, one end of each of saidpassages opening adjacent said web; a source of air connected to theopposite end of said passages to thereby form an air film between saidelectrode holders and said web; a plurality of electrodes individuallycarried by said plurality of electrode holders; a source ofradio-frequency energy connected to said electrodes; an arcuateenclosure radially spaced from said arcuate supporting member to definea closed volume therebetween through which said web is directed; aplurality of air emitting nozzles located on the interior of saidarcuate enclosure and directed toward said web; a controllable source ofheated air connected to said plurality of air 3 ,722,'105 5 6 emittingnozzles to balance the force on said web of the passages in saidelectrode holders and said source of air film gellerated y Said airemitting P g j air, said switch being connected to said source of radiothrough said electrode holders, thereby controlling the frequency energyto deactivate Said source of radio elevation of said web above saidelectrode holders; means for exhausting the air from said arcuateenclo-'5 frequency energy when sald Sensmg element Indicates a decr ase in airess r sure; and an air pressure sensitive switch having a e pr u esensing element located intermediate said air emitting

1. The method of applying radio frequency energy to a moving web ofmaterial comprising the steps of diverting said web from its normal pathof travel into an arcuate path, floating said web on an air film over aplurality of electrodes located about the periphery of said path,applying radio frequency energy to said web from said electrodes as saidfilm floats over said electrodes, sensing the pressure of said air film,signaling a decrease in the pressure of said air film, discontinuingapplication of said radio frequency energy in response to said decreasedpressure signal, and returning said web to its normal path of travel. 2.The method of claim 1, further including the steps of directing air atsaid web on the side of said web opposite said air film through aplurality of air emitting nozzles, and positioning said web above saidelectrodes in response to the pressure differential between said airfilm and the air directed by said plurality of nozzles.
 3. The method ofClaim 2 wherein said air in said air film and said air directed throughsaid air emitting nozzles is heated to a temperature greater thanambient air temperature.
 4. Apparatus for applying radio frequencyenergy to a moving web of material directed in an arcuate pathcomprising, in combination: an arcuate supporting member defining thearcuate path for said web; a plurality of electrode holders arrangedabout the periphery of said arcuate supporting member, each of saidelectrode holders having a plurality of passages formed therethrough,one end of each of said passages opening adjacent said web; a source ofair connected to the opposite end of said passages to thereby form anair film between said electrode holders and said web; a plurality ofelectrodes individually carried by said plurality of electrode holders;a source of radio-frequency energy connected to said electrodes; anarcuate enclosure radially spaced from said arcuate supporting member todefine a closed volume therebetween through which said web is directed;a plurality of air emitting nozzles located on the interior of saidarcuate enclosure and directed toward said web; a controllable source ofheated air connected to said plurality of air emitting nozzles tobalance the force on said web of the air film generated by said airemitting passages formed through said electrode holders, therebycontrolling the elevation of said web above said electrode holders;means for exhausting the air from said arcuate enclosure; and an airpressure sensitive switch having a sensing element located intermediatesaid air emitting passages in said electrode holders and said source ofair, said switch being connected to said source of radio frequencyenergy to deactivate said source of radio frequency energy when saidsensing element indicates a decrease in air pressure.